Field of the invention and description of prior art
[0001] The invention relates to a method for forming a pattern on a surface of a substrate
or target by means of a beam of energetic electrically charged particles. More in
detail, the invention relates to a method for irradiating a target with a beam of
energetic radiation comprising electrically charged particles, comprising the steps
of
- providing a pattern definition device having a plurality of apertures transparent
to said radiation,
- illuminating said pattern definition device by means of an illuminating wide beam,
which traverses the pattern definition device through said apertures thus forming
a patterned beam consisting of a corresponding plurality of beamlets,
- forming said patterned beam into a pattern image on the location of the target, said
pattern image comprising the images of at least part of the plurality of apertures
covering a number of pattern pixels on the target, and
- generating a relative movement between said target and the pattern definition device
producing a movement of said pattern image on the target along a path over a region
where a beam exposure is to be performed, said path being composed of sections which
each extend along a general direction, said region being composed of a plurality of
pattern pixels arranged in a regular arrangement and said region having a total width
as measured across said general direction, the movement along said path defining a
number of stripes covering said region in sequential exposures.
[0002] Methods of the above-described type and charged-particle multi-beam processing apparatuses
employing such methods are well-known in prior art. In particular, the applicant has
realized charged-particle multi-beam devices as described in several patents in the
name of the applicant with respect to the charged-particle optics, pattern definition
(PD) device, and multi-beam writing methods employed therein. For instance, a 50 keV
electron multi-beam writer which allows to realize leading-edge complex photomasks
for 193nm immersion lithograph, of masks for EUV lithography and of templates (1x
masks) for imprint lithography, has been implemented, called eMET (electron Mask Exposure
Tool) or MBMW (multi-beam mask writer), for exposing 6" mask blank substrates. Moreover,
a multi-beam system also referred to as PML2 (Projection Mask-Less Lithography) was
implemented for electron beam direct write (EBDW) applications on Silicon wafer substrates.
Multi-beam processing apparatuses of the said kind are hereinafter referred to as
multi-beam writer, or short MBW.
[0003] As a typical implementation of an MBW, the applicant has realized a 50 keV electron
writer tool implementing a total beam size of 20 nm comprising 512 × 512 (= 262,144)
programmable beamlets within a beam array field of dimensions 81.92 µm × 81.92 µm
at the substrate. In this system, which is referred to as "MBMW tool" hereinafter,
the substrate is, typically, a 6" mask blank (having an area of 6" × 6" = 152.4 mm
× 152.4 mm and thickness 6"/4 = 6.35 mm) covered with an electron beam sensitive resist;
furthermore, multi-beam writing is possible on resist-covered 150 mm Si wafers as
well.
[0004] The current density of a typical MBW, such as the MBMW tool, is no higher than 1
A/cm
2 when using 20nm beam size. Thus, when all programmable 262,144 beamlets are "on"
the maximum current is 1.05 µA. In this implementation the 1 sigma blur of the MBW
column is approx. 5 nm, as verified experimentally.
[0005] There is the possibility to change the beam size, e.g., from 20 nm to 10 nm. For
a column with 200:1 reduction this is straightforward by using a different aperture
array plate (AAP), with 2 µm × 2 µm opening size of the apertures instead of 4 µm
× 4 µm opening size. As outlined in
US 8,546,767 of the applicant, a change of the beam size may also be realized in-situ by spatial
adjustment of the AAP having multiple aperture arrays of different geometric parameters,
such a total size, aperture spacing, aperture shapes etc.
[0006] When using a 10 nm beam size and providing a current density at the substrate of
no higher than 4 A/cm
2, the current of 262,144 programmable beamlets (with all beamlets "on") is again 1.05
µA at maximum. Thus, also in this case there is virtually no change of the 1 sigma
blur of the column with current through the column.
[0007] The first generation MBW production machines are targeted to use 20nm and 10nm beams
providing up to approx. 1 µA current for all 262,144 programmable beams "on". For
following generations of MBW production machines there is the plan to use even smaller
beam size, for instance of 8 nm, and concurrently to provide e.g. 640 × 640 = 409,600
beamlets within the 81.92 µm × 81.92 µm beam array field at the substrate. Keeping
the maximum current density at 4 A/cm
2 will ensure that the maximum current (with all beamlets "on") is 1.05 µA. For instance,
using a 5 nm beam size allows providing e.g. 1024 × 1024 = 1,048,576 programmable
beams within the mentioned beam array field at the substrate; again, at a maximum
current density of 4 A/cm
2 the maximum current (with all beamlets "on") is 1.05 µA.
[0008] For industrial applications, very demanding MBW performance requirements are imposed
with respect to achieving a small Critical Dimension (CD) and, in particular, to achieving
3sigma or 6sigma variations at a nanometer level of the Local CD Uniformity (LCDU)
within small fields (e.g. the area of the MBW beam array field) as well as nanometer
level 3sigma or 6sigma variations of the Global CD Uniformity (GCDU) over the whole
MBW writing field on a substrate (e.g. a 6" mask blank or a 300mm Silicon wafer).
[0009] Furthermore, it is desired to fine-adjust the line edge position by means of a specifically
adapted exposure dose profile. Furthermore, such a fine-adjustment should not only
be adaptable within the MBW beam array field (local) but also over the whole MBMW
writing field on a substrate (global).
[0010] Using the MBW architecture of the applicant, low CD values can be achieved and small
LCDU and GCDU values. However, in order to fulfill the very demanding MBW specifications
of very low LCDU and GCDU values, there is the need for additional fine corrections.
Here, the terms "local" and "global" refer again to small fields (e.g. the area of
the MBW beam array field) and the whole MBW writing field on a substrate, respectively.
[0011] Patent US 8,378,320 B2 of the applicant describes a multi-beam writing method, which may be designated "Single-Pass-with-Soft-Butting",
where the target (substrate) is exposed in a sequence of exposure stripes. The exposure
stripes are realized by mechanically scanning the substrate in one direction (e.g.:
+X) and in the opposite direction (-X) by means of a target stage on which the target
is placed. In order to move from one stripe exposure to the next, the substrate is
moved in the perpendicular direction by a distance which corresponds to the stripe
width or, in the case of overlapping stripes, by a smaller amount depending on the
stripe overlap chosen. The stage velocity in the stripe exposure direction is high,
i.e. in the order of mm/s. A high stage velocity in the stripe exposure direction
is mandatory to achieve an acceptable writing time due to the long stripe length (e.g.
132mm when exposing a mask field of 132mm × 104mm). On the other hand, the stage velocity
in the other direction need not be high since the maximal distance is the stripe width,
which is about 0.1mm. For example, in the MBW tool realized by the applicant the beam
array field at the substrate covers an area of c. 82µm × 82µm and thus the exposure
stripe has a width of 82µm in this case.
[0012] As outlined in
US 2015/0028230 A1 of the applicant, even better reduction of stripe butting errors may be achieved
by implementing a multi-beam exposure method, which could be termed "Double-Pass-at-50%-Overlap",
where the first set of stripes is exposed with half of the exposure spots whereas
the second set of stripes is exposed with 50% overlay, again with half of the exposure
spots. Thus, both sets of stripe exposures together realize the pattern with the desired
exposure dose. As also pointed out in the above cited patent application, the sequence
of stripe writing may be chosen to strongly reduce resist heating, resist charging
and substrate heating effects by employing a "Multiple-Stripes" method, where the
exposure is split into multiple stripes distributed across the plate by predefined
sequence and distribution. The Multiple-Stripes method can be implemented for various
writing techniques, including Single-Pass-with-Soft-Butting and Double-Pass-at-50%-Overlap;
it can also be combined with the writing methods of the present invention.
[0013] Although the previously mentioned methods of the applicant from
US 8,378,320 B2 and
US 2015/0028230 A1 already yield a distinct improvement of the writing quality of the MBW tool, a further
enhancement is still desirable. In particular there is always a need for further reducing
misplacements through an increased level of averaging over the beam array field. Since
there are increasingly tightened demands on Local and Global Critical Dimension Uniformity,
LCDU and GCDU, respectively, and also on local and global pattern placement accuracy
("Registration"), additional innovations are necessary as described below.
[0014] In view of the above, it is an objective of the present invention to overcome these
shortcomings of prior art.
Summary of the invention
[0015] The above-mentioned objective is met by a method according to claim 1 and as described
in the beginning wherein the number of stripes is written in at least two sweeps,
which each have a respective general direction, but the general direction being changed
between sweeps. It is important to note that the term "general direction" is meant
to include both ways of moving along a given direction on the target plane. Each stripe
belongs to exactly one of said sweeps, and runs substantially parallel to the other
stripes of the same sweep, namely, along the respective general direction. The stripes
have respective widths as measured across said main direction, and for each sweep
the widths of the stripes of one sweep will combine into a cover of the total width
(i.e., the width of the region to be exposed when measured across the respective general
direction). Thus, one sweep has at least one stripe written along a respective general
direction which is at an angle (non-trivial angle, i.e. greater than 0° and up to
90°) to that of the respective previous sweep; and in one suitable special case, the
angle between general directions of consecutive sweeps is a right angle (90°). The
number of sweeps is usually two, or may be an even number, in particular in the case
of two general directions at a right angle; generally, however, any number of sweeps
may be possible.
[0016] Conventional vacuum X-Y stages usually have the capability of high stage velocity
in one direction only. This is adequate for the multi-beam exposure of stripes as
outlined above. Recently, however, an air-bearing X-Y vacuum stage became available
which has the capability of high stage velocity in X as well as in Y direction. This
stage, in combination with an MBW tool as described above, allows to adopt a "Bi-Directional"
multi-beam writing method to achieve improved LCDU, and GCDU, as well as local and
global Registration.
[0017] This method according to the invention allows the adoption of a multi-beam writing
method which will be referred to as "Bi-Directional-Double-Pass" in short. With this
method, there is efficient averaging of local beam-to-substrate errors and beam array
field errors by complete stripe boundary overlap strongly reducing influences of stage
noise, beam array field distortion, beam blur distribution and exposure dose inhomogeneity.
Thus, the Bi-Directional-Double-Pass represents a considerable improvement to achieve
superior multi-beam writing performance.
[0018] It is important to note that the "Bi-Directional-Double-Pass" multi-beam writing
method of the invention can be implemented without degrading the exposure field write
time. The reason is that all exposures can be done at twice the stage velocity as
compared to prior methods, in particular the Single-Pass-with-Soft-Butting method.
[0019] The exposure with doubled stage velocity is beneficial to reduce local resist and
substrate heating and to diminish resist charging.
[0020] In an advantageous development of the invention, each sweep may be associated with
one of a number of partial grids of pattern pixels which are exposable during the
respective sweep, the partial grids being mutually different and, when taken together,
combining to the complete plurality of pattern pixels which are comprised in said
region where a beam exposure is to be performed.
[0021] The groups of stripes belonging to the same sweep are usually written subsequently
in time, i.e., in immediate order.
[0022] Moreover, a further reduction of time needed for the writing process may be obtained
when stripes written with the same general direction are written with alternating
orientation of said general direction.
[0023] Furthermore, the stripes of each sweep may suitably have uniform width.
[0024] Within each sweep the stripes may be exposed at lateral offsets to each other which
correspond to the respective widths of the stripes. Alternatively, the stripes of
at least one of the sweeps, preferably of all sweeps, may be overlapping. In the overlapping
case, wherein in the range of overlap of two stripes of the same sweep: nominal positions
of pattern pixels of one of the two stripes are overlapping with nominal positions
of corresponding pattern pixels of the other of the two stripes, and pattern pixels
are exposed in the two overlapping stripes in a complementary manner with regard to
the pattern to be imposed.
[0025] In the case that a sweep contains a plurality of stripes to be written, the stripes
may be arranged on the target region side by side but in a non-consecutive temporal
order. In this case, the plurality of stripes of each sweep may be distributed into
at least two groups of spatially adjacent stripes, and the stripes are written either
in a time sequence wherein either each stripe is followed by a non-adjacent stripe
of a different group, or in a time sequence wherein the stripes are written in groups
of stripes according to the order of the groups, with each group of stripes being
followed by a non-adjacent different group.
[0026] The above-mentioned objective is also achieved by a charged-particle multi-beam processing
apparatus for exposure of a target by means of a structured beam of electrically charged
particles, comprising an illumination system, a pattern definition device, a projection
optics system, and a target stage. The illumination system is configured to produce
a beam of said electrically charged particles and form it into an illuminating wide
beam illuminating the pattern definition device; the pattern definition device is
configured to form the shape of the illuminating beam into a patterned beam composed
of a plurality of beamlets; and the projection optics system is configured to form
said patterned beam into a pattern image on the location of the target, thus exposing
a plurality of pattern pixels on the target; moreover, the target stage is configured
to generate a relative movement between said target and the pattern definition device,
so the apparatus is enabled to perform the method according to the invention as described
above.
[0027] In this context, it is additionally suitable to use a target stage which is configured
to move and fine position the target along at least two of the general directions.
This means that, in particular, the target stage is configured to continuously move
the target along at least two of the general directions, wherein any offset from a
nominal position, which offset (i.e., the difference between the actual and the nominal
position) may occur during a movement by a first distance along either of said at
least two of the general directions, is always less than a small fraction of the first
distance, where the fraction is preferably equal to or in the order of 0.001. The
length of a first distance will generally correspond to the distance covered in a
typical time such as one second, or the length or the width of one stripe. For instance,
it may be advantageous to enable high stage velocity in an X and a Y direction in
the target plane, where high velocity means that it is sufficient to enable a speed
sufficient for writing a stripe; for instance a velocity of at least 1 mm/s, or even
at least 3.5 mm/s. For instance, the target stage may comprise air bearings. Such
target stage can advantageously contribute to an efficient way of generating the relative
movement between the target and the pattern definition device.
Brief description of the drawings
[0028] In the following, the present invention is described in more detail with reference
to the drawings, which schematically show:
- Fig. 1
- a MBW system of state of the art in a longitudinal sectional view;
- Fig. 2
- a pattern definition system state of the art in a longitudinal section;
- Fig. 3
- illustrates the basic writing strategy on the target using stripes;
- Fig. 4
- shows an exemplary arrangement of apertures as imaged onto the target;
- Fig. 5
- shows an example of a pixel map of an exemplary pattern to be exposed;
- Fig. 6A
- illustrates an arrangement of apertures with M=2, N=2;
- Fig. 6B
- shows an example of oversampling of the pixels in a "double grid" arrangement;
- Fig. 7A
- illustrates the exposure of one stripe;
- Fig. 7B
- shows the stripe resulting from the process of Fig. 7A;
- Fig. 7c
- shows two overlapping strips of different passes;
- Figs. 8A-C
- show three different cases of grid placements, namely Fig. 8A: "Double Grid", Fig.
8B: "Quad Grid", and Fig. 8C: "Double-Centered Grid";
- Fig. 9
- illustrate the intensity profile which is generated when one single exposure spot
is exposed with a maximum dose;
- Fig. 10
- illustrates an intensity profile of the MBW of the type shown in Fig. 1, and a dose
level profile for a 30 nm line;
- Fig. 11
- shows an intensity profile for the 30 nm line dose level profile of Fig. 10;
- Figs. 12A,B
- illustrate MBW intensity profiles and related data as obtained for a simulation of
a line, with a line width of 31.4 nm (Fig. 12A) and 40.0 nm (Fig. 12B), respectively.
- Fig. 13
- illustrates the generation of a 30nm line with the MBW;
- Fig. 13A
- shows a detail of Fig. 13 at the left-hand flank where the intensity profiles crosses
the "0.5" intensity level;
- Fig. 14A
- illustrates the intensity profile generated from the exposure of a line of a determined
width;
- Figs. 14B,C
- illustrate the fine adjustment of the position of one edge (Fig. 14B) or both edges
(Fig. 14c) of the line of Fig. 14A via suitable modifications of the dose levels corresponding
the exposure spots;
- Figs. 15
- shows an example of the arrangement of stripes to be exposed according to the "Double-Pass-at-50%-Overlap"
exposure method;
- Fig. 16
- illustrates the arrangement of exposure spots according to two partial grids with
the exposure method shown in Fig. 15 for a "Double-Grid";
- Figs. 16A,B
- demonstrate the graphical representation of the exposure spots shown in Fig. 16, for
the first and second pass, respectively;
- Fig. 17
- illustrates the arrangement of exposure spots according to two partial grids with
the exposure method of Fig. 15 for a "Centered-Double-Grid";
- Fig. 18
- illustrates the arrangement of exposure spots according to two partial grids with
the exposure method of Fig. 15 for a "Quad-Grid";
- Fig. 19
- illustrates the arrangement of exposure spots written in the stripes of a first pass
of Fig. 18;
- Figs. 19A,B
- show the graphical representation of the exposure spots used in Fig. 19, for the odd-numbered
and even-numbered stripes, respectively, of the first pass;
- Figs. 20
- illustrates the arrangement of exposure spots written in the stripes of a second pass
of Fig. 18;
- Figs. 20A,B
- show the graphical representation of the exposure spots used in Fig. 20, for the odd-numbered
and even-numbered stripes, respectively, of the second pass;
- Fig. 21
- shows the combined exposure spots of Figs. 19 and 20;
- Fig. 22
- shows an example of an arrangement of stripes arranged along multiple directions,
as an example of a "Bi-Directional-Double-Pass" exposure method;
- Fig. 23
- illustrates the arrangement of exposure spots according to partial grids with the
method illustrated in Fig. 22; and
- Figs. 24A,B
- illustrates a variant of the chronology of writing the stripes that are oriented along
a given direction, with Fig. 24A showing the sequence for the stripes of a first run,
and Fig. 24B showing the stripes of a second run in addition to those of the first
run of Fig. 24A.
Detailed description of the invention
[0029] It should be appreciated that the invention is not restricted to the embodiments
discussed in the following, which merely represent suitable implementations of the
invention.
Lithographic Apparatus
[0030] An overview of a lithographic apparatus suitable to employ the preferred embodiment
of the invention is shown in Fig. 1. In the following, only those details are given
as needed to disclose the invention; for the sake of clarity, the components are not
shown to size in Fig. 1. The main components of the lithography apparatus 1 are -
corresponding to the direction of the lithography beam lb, pb which in this example
runs vertically downward in Fig. 1 - an illumination system 3, a pattern definition
(PD) system 4, a projecting system 5, and a target station 6 with the substrate 16.
The whole apparatus 1 is contained in a vacuum housing 2 held at high vacuum to ensure
an unimpeded propagation of the beam lb, pb of charged particles along the optical
axis cw of the apparatus. The charged-particle optical systems 3, 5 are realized using
electrostatic and/or magnetic lenses.
[0031] The illumination system 3 comprises, for instance, an electron gun 7, an extraction
system 8 as well as a condenser lens system 9. It should, however, be noted that in
place of electrons, in general, other electrically charged particles can be used as
well. Apart from electrons these can be, for instance, hydrogen ions or heavier ions,
charged atom clusters, or charged molecules.
[0032] The extraction system 8 accelerates the particles to a defined energy of typically
several keV, e.g. 5 keV. By means of a condenser lens system 9, the particles emitted
from the source 7 are formed into a broad, substantially telecentric particle beam
50 serving as lithography beam lb. The lithography beam lb then irradiates a PD system
4 which comprises a number of plates with a plurality of openings (also referred to
as apertures). The PD system 4 is held at a specific position in the path of the lithography
beam lb, which thus irradiates the plurality of apertures and/or openings and is split
into a number of beamlets.
[0033] Some of the apertures/openings are "switched on" or "open" so as to be transparent
to the incident beam in the sense that they allow the portion of the beam that is
transmitted through it, i.e. the beamlets 51, to reach the target; the other apertures/openings
are "switched off" or "closed", i.e. the corresponding beamlets 52 cannot reach the
target, and thus effectively these apertures/openings are non-transparent (opaque)
to the beam. Thus, the lithography beam lb is structured into a patterned beam pb,
emerging from the PD system 4. The pattern of switched on apertures - the only portions
of the PD system 4 which are transparent to the lithography beam lb - is chosen according
to the pattern to be exposed on the substrate 16 covered with charged-particle sensitive
resist 17. It has to be noted that the "switching on/off" of the apertures/openings
is usually realized by a suitable type of deflection means provided in one of the
plates of the PD system 4: "Switched off" beamlets 52 are deflected off their path
(by sufficient albeit very small angles) so they cannot reach the target but are merely
absorbed somewhere in the lithography apparatus, e.g. at an absorbing plate 11.
[0034] The pattern as represented by the patterned beam pb is then projected by means of
an electro-magneto-optical projection system 5 onto the substrate 16 where the beam
forms an image of the "switched-on" apertures and/or openings. The projection system
5 implements a demagnification of, for instance, 200:1 with two crossovers c1 and
c2. The substrate 16 is, for instance, a 6" mask blank or a silicon wafer covered
with a particle sensitive resist layer 17. The substrate is held by a chuck 15 and
positioned by a substrate stage 14 of the target station 6. The substrate stage 14
is, for instance, an air-bearing X-Y vacuum stage able to perform high stage velocity
in X as well as in Y direction.
[0035] The information regarding the pattern to be exposed is supplied to the PD system
4 by the data path realized by means of an electronic pattern information processing
system 18. The data path is explained further below in section "Datapath".
[0036] In the embodiment shown in Fig. 1, the projection system 5 is composed of a number
of consecutive electro-magneto-optical projector stages 10a, 10b, 10c, which preferably
include electrostatic and/or magnetic lenses, and possibly other deflection means.
These lenses and means are shown in symbolic form only, since their application is
well known in the prior art. The projection system 5 employs a demagnifying imaging
through crossovers c1, c2. The demagnification factor for both stages is chosen such
that an overall demagnification of several hundred results, e.g. 200:1 reduction.
A demagnification of this order is in particular suitable with a lithography setup,
in order to alleviate problems of miniaturization in the PD device.
[0037] In the whole projection system 5, provisions are made to extensively compensate the
lenses and or deflection means with respect to chromatic and geometric aberrations.
As a means to shift the image laterally as a whole, i.e. along a direction perpendicular
to the optical axis cw, deflection means 12a, 12b and 12c are provided in the condenser
3 and projection system 5. The deflection means may be realized as, for instance,
a multipole electrode system which is either positioned near the source extraction
system 12a or one of the crossovers, as shown in Fig. 1 with the deflection means
12b, or after the final lens 10c of the respective projector, as in the case with
the stage deflection means 12c in Fig. 1. In this apparatus, a multipole electrode
arrangement is used as deflection means both for shifting the image in relation to
the stage motion and for correction of the imaging system in conjunction with the
charge-particle optics alignment system. These deflection means 10a, 10b, 10c are
not to be confused with the deflection array means of the PD system 4 in conjunction
with the stopping plate 11, as the latter are used to switch selected beamlets of
the patterned beam pd "on" or "off", whereas the former only deal with the particle
beam as a whole. There is also the possibility to rotate the ensemble of programmable
beams using a solenoid 13 providing an axial magnetic field.
[0038] The sectional detail of Fig. 2 illustrates one suitable embodiment of a PD system
4, which comprises three plates stacked in a consecutive configuration: An "Aperture
Array Plate" (AAP) 20, a "Deflection Array Plate" (DAP) 30 and a "Field-boundary Array
Plate" (FAP) 40. It is worthwhile to note that the term 'plate' refers to an overall
shape of the respective device, but does not necessarily indicate that a plate is
realized as a single plate component even though the latter is usually the preferred
way of implementation; still, in certain embodiments, a 'plate', such as the aperture
array plate, may be composed of a number of sub-plates. The plates are preferably
arranged parallel to each other, at mutual distances along the Z direction (vertical
axis in Fig. 2).
[0039] The flat upper surface of AAP 20 forms a defined potential interface to the charged-particle
condenser optics/illumination system 3. The AAP may, e.g. be made from a square or
rectangular piece of a silicon wafer (approx. 1mm thickness) 21 with a thinned center
part 22. The plate may be covered by an electrically conductive protective layer 23
which will be particularly advantageous when using hydrogen or helium ions (line in
US 6,858,118). When using electrons or heavy ions (e.g. argon or xenon), the layer 23 may also
be of silicon provided by the surface section of 21 and 22, respectively, so that
there is no interface between layer 23 and the bulk parts 21, 22.
[0040] The AAP 20 is provided with a plurality of apertures 24 formed by openings traversing
the thinned part 22. The apertures 24 are arranged in a predetermined arrangement
within an aperture area provided in the thinned part 22, thus forming an aperture
array 26. The arrangement of the apertures in the aperture array 26 may be, for instance,
a staggered arrangement or a regular rectangular or square array (cf. Fig. 4). In
the embodiment shown, the apertures 24 are realized having a straight profile fabricated
into the layer 23 and a "retrograde" profile in the bulk layer of the AAP 20 such
that the downward outlets 25 of the openings are wider than in the main part of the
apertures 24. Both the straight and retrograde profiles can be fabricated with state-of-the-art
structuring techniques such as reactive ion etching. The retrograde profile strongly
reduces mirror charging effects of the beam passing through the opening.
[0041] The DAP 30 is a plate provided with a plurality of openings 33, whose positions correspond
to those of the apertures 24 in the AAP 20, and which are provided with electrodes
35, 38 configured for deflecting the individual beamlets passing through the openings
33 selectively from their respective paths. The DAP 30 can, for instance, be fabricated
by post-processing a CMOS wafer with an ASIC circuitry. The DAP 30 is, for instance,
made from a piece of a CMOS wafer having a square or rectangular shape and comprises
a thicker part 31 forming a frame holding a center part 32 which has been thinned
(but may be suitably thicker as compared to the thickness of 22). The aperture openings
33 in the center part 32 are wider compared to 24 (by approx. 2µm at each side for
instance). CMOS electronics 34 is provided to control the electrodes 35,38, which
are provided by means of MEMS techniques. Adjacent to each opening 33, a "ground"
electrode 35 and a deflection electrode 38 are provided. The ground electrodes 35
are electrically interconnected, connected to a common ground potential, and comprise
a retrograde part 36 to prevent charging and an isolation section 37 in order to prevent
unwanted shortcuts to the CMOS circuitry. The ground electrodes 35 may also be connected
to those parts of the CMOS circuitry 34 which are at the same potential as the silicon
bulk portions 31 and 32.
[0042] The deflection electrodes 38 are configured to be selectively applied an electrostatic
potential; when such electrostatic potential is applied to an electrode 38, this will
generate an electric field causing a deflection upon the corresponding beamlet, deflecting
it off its nominal path. The electrodes 38 as well may have a retrograde section 39
in order to avoid charging. Each of the electrodes 38 is connected at its lower part
to a respective contact site within the CMOS circuitry 34.
[0043] The height of the ground electrodes 35 is higher than the height of the deflection
electrodes 38 in order to suppress cross-talk effects between the beamlets.
[0044] The arrangement of a PD system 4 with a DAP 30 shown in Fig. 2 is only one of several
possibilities. In a variant (not shown) the ground and deflection electrodes 35, 38
of the DAP may be oriented upstream (facing upward), rather than downstream. Further
DAP configurations, e.g. with embedded ground and deflection electrodes, can be devised
by the skilled person (see other patents in the name of the applicant, such as
US 8,198,601 B2).
[0045] The third plate 40 serving as FAP has a flat surface facing to the first lens part
of the downstream demagnifying charged-particle projection optics 5 and thus provides
a defined potential interface to the first lens 10a of the projection optics. The
thicker part 41 of FAP 40 is a square or rectangular frame made from a part of a silicon
wafer, with a thinned center section 42. The FAP 40 is provided with a plurality of
openings 43 which correspond to the openings 24, 33 of the AAP 20 and DAP 30 but are
wider as compared to the latter.
[0046] The PD system 4, and in particular the first plate of it, the AAP 20, is illuminated
by a broad charged particle beam 50 (herein, "broad" beam means that the beam is sufficiently
wide to cover the entire area of the aperture array formed in the AAP), which is thus
divided into many thousands of micrometer-sized beamlets 51 when transmitted through
the apertures 24. The beamlets 51 will traverse the DAP and FAP unhindered.
[0047] As already mentioned, whenever a deflection electrode 38 is powered through the CMOS
electronics, an electric field will be generated between the deflection electrode
and the corresponding ground electrode, leading to a small but sufficient deflection
of the respective beamlet 52 passing through (Fig. 2). The deflected beamlet can traverse
the DAP and FAP unhindered as the openings 33 and 43, respectively, are made sufficiently
wide. However, the deflected beamlet 52 is filtered out at the stopping plate 11 of
the sub-column (Fig. 1). Thus, only those beamlets which are unaffected by the DAP
will reach the substrate.
[0048] The reduction factor of the demagnifying charged-particle optics 5 is chosen suitably
in view of the dimensions of the beamlets and their mutual distance in the PD device
4 and the desired dimensions of the structures at the target. This will allow for
micrometer-sized beamlets at the PD system whereas nanometer-sized beamlets are projected
onto the substrate.
[0049] The ensemble of (unaffected) beamlets 51 as formed by AAP is projected to the substrate
with a predefined reduction factor R of the projection charged-particle optics. Thus,
at the substrate a "beam array field" (BAF) is projected having widths BX = AX/R and
BY = AY/R, respectively, where AX and AY denote the sizes of the aperture array field
along the X and Y directions, respectively. The nominal width of a beamlet at the
substrate (i.e. aperture image) is given by bX = aX/R and bY = aY/R, respectively,
where aX and aY denote the sizes of the beamlet 51 as measured along the X and Y directions,
respectively, at the level of the DAP 30.
[0050] It is worthwhile to note that the individual beamlets 51, 52 depicted in Fig. 2 represent
a much larger number of beamlets, typically many thousands, arranged in a two-dimensional
X-Y array. The applicant has, for instance, realized multi-beam charged-particle optics
with a reduction factor of R = 200 for ion as well as electron multi-beam columns
with many thousands (e.g., 262,144) programmable beamlets. The applicant has realized
such columns with a BAF of approx. 82µm × 82µm at the substrate. These examples are
stated for illustrative purpose, but are not to be construed as limiting examples.
[0051] Referring to Fig. 3, a pattern image pm as defined by the PD system 4 is produced
on the target 16. The target surface covered with the charged-particle sensitive resist
layer 17 will comprise one or more areas R1 to be exposed. Generally, the pattern
image pm exposed on the target has a finite size y0 which is usually well smaller
than the width of the area R1 which is to be patterned. Therefore, a scanning stripe
exposure strategy is utilized, where the target is moved under the incident beam,
so as to change the position of the beam on the target perpetually: the beam is effectively
scanned over the target surface. It is emphasized that for the purpose of the invention
only the relative motion of the pattern image pm on the target is relevant. By virtue
of the relative movement the pattern image pm is moved over the area R1 so as to form
a sequence of stripes s1, s2, s3, ... sn (exposure stripes). of width y0. The complete
set of stripes covers the total area of the substrate surface. The scanning direction
sd may be uniform or may alternate from one stripe to the next.
[0052] Fig. 5 shows a simple example of an imaged pattern ps with a size of 10x16 =180 pixels,
where some pixels p100 of the exposure area are exposed to a gray level 401 of 100%
and other pixels p50 are exposed 402 to only 50% of the full gray level. The remaining
pixels are exposed to a 0% dose 403 (not exposed at all). Of course, in a realistic
application of the invention, the number of pixels of the standard image would be
much higher. However, in Fig. 5 the number of pixels is only 180 for the better clarity.
Also, in general, much more gray levels will be used within the scale from 0% to 100%.
[0053] Thus, the pattern image pm (Fig. 3) is composed of a plurality of pattern pixels
px, which are exposed with dose values according to the desired pattern to be exposed.
It should be appreciated, however, that only a subset of the pixels px can be exposed
simultaneously since only a finite number of apertures is present in the aperture
field of the PD system. The pattern of switched-on apertures is chosen according to
the pattern to be exposed on the substrate. Thus, in an actual pattern not all pixels
are exposed at the full dose, but some pixels will be "switched off" in accordance
with the actual pattern; for any pixel (or, equivalently, for every beamlet covering
the pixel) the exposure dose can vary from one pixel exposure cycle to the next whether
the pixel is "switched on" or "switched off", depending on the pattern to be exposed
or structured on the target.
[0054] While the substrate 16 is moved continuously, the same image element corresponding
to a pattern pixel px on the target may be covered many times by the images of a sequence
of apertures. Simultaneously, the pattern in the PD system is shifted, step by step,
through the apertures of the PD system. Thus, considering one pixel at some location
on the target, if all apertures are switched on when they cover that pixel, this will
result in the maximum exposure dose level: a "white" shade corresponding to 100%.
In addition to a "white" shade, it is possible to expose a pixel at the target according
to a lower dose level (also dubbed 'gray shade') which would interpolate between a
the minimal ('black') and maximal ('white') exposure dose levels. A gray shade may,
for instance, be realized by switching on only a subset of apertures that may be involved
in writing one pixel; for example, 4 out of 16 apertures would give a gray level of
25%. Another approach is reducing the duration of unblanked exposure for the apertures
involved. Thus, the exposure duration of one aperture image is controlled by a gray
scale code, for example an integer number. The exposed aperture image is the manifestation
of one of a given numbers of gray shades that correspond to zero and the maximum exposure
duration and dose level. The gray scale usually defines a set of gray values, for
instance 0,1/(n
y-1) ..., i/(n
y-1), ...,1 with n
y being the number of gray values and i an integer ("gray index", 0≤i≤n
y-1). Generally, however, the gray values need not be equidistant and form a non-decreasing
sequence between 0 and 1.
[0055] Fig. 4 shows the arrangement of apertures in the aperture field of the PD device,
according to a basic layout and also illustrates several quantities and abbreviations
used in the following. Shown is the arrangement of the aperture images b1 as projected
onto the target, shown in dark shades. The main axes X and Y correspond to the direction
of advance of the target motion (scanning direction sd) and the perpendicular direction,
respectively. Each aperture image has widths bX and bY along the directions X and
Y respectively. The apertures are arranged along lines and rows having MX and MY apertures,
respectively, with the offset between neighboring apertures in a line and row being
NX and NY respectively. As a consequence, to each aperture image belongs a conceptual
cell C1 having an area of NX·bX·NY·bY, and the aperture arrangement contains MX·MY
cells arranged in a rectangular way. In the following, these cells C1 are referred
to as "exposure cells". The complete aperture arrangement, as projected onto the target,
has dimensions of BX = MX·NX·bX by BY = MY·NY·bY. In the discussion hereinafter, we
will assume a square grid as a special case of a rectangular grid, and set b = bX
= bY, M = MX = MY, and N = NX = NY with M being an integer, for all further explanations
without any restriction of the generality. Thus, an "exposure cell" has a size of
N·b×N·b on the target substrate.
[0056] The distance between two neighboring exposure positions is denoted as
e in the following. In general, the distance
e can be different from the nominal width b of an aperture image. In the simplest case,
b = e, which is illustrated in Fig. 6A for the example of an arrangement of 2×2 exposure
cells C3, and one aperture image bi0 covers (the nominal position of) one pixel. In
another interesting case, illustrated in Fig. 6B (and in line with the teachings of
US 8,222,621 and
US 7,276,714),
e may be a fraction b/
o of the width b of the aperture image, with
o>1 being preferably (but not necessarily) an integer which we also refer to as the
oversampling factor. In this case the aperture images, in the course of the various
exposures, will spatially overlap, allowing a higher resolution of the placement of
the pattern to be developed. It follows that each image of an aperture will, at one
time, cover multiple pixels, namely
o2 pixels. The entire area of the aperture field as imaged to the target will comprise
(NM
o)
2 pixels. From the point of view of placement of aperture image, this oversampling
corresponds to a so-called placement grid which is different (since it is finer in
spacing) than what would be necessary to simply cover the target area.
[0057] Fig. 6B illustrates one example of an oversampling of
o=2 combined with placement grids. Namely, the image of an aperture array with an exposure
cell C4 having parameters
o=2, N=2. Thus, on each nominal location (small square fields in Fig. 6B) four aperture
images bi1 (dashed lines) are printed, which are offset on a regular grid by pitch
e in both X and Y directions. While the size of the aperture image still is of the
same value b, the pitch
e of the placement grid is now b/
o = b/2. The offset to the previous nominal location (offset of the placement grid)
is also of size b/2. At the same time, the dose and/or the gray shade of each pixel
may be adapted (reduced), by choosing suitable gray value for the aperture image that
cover the respective pixel. As a result, an area of size a is printed but with an
enhanced placement accuracy due to the finer placement grid. Direct comparison of
Fig. 6B with Fig. 6A shows that locations of aperture images are just arranged on
a placement grid twice (generally, o times) as fine as before, while the aperture
images themselves overlap. The exposure cell C4 now contains (N
o)
2 locations (i.e., "pixels") to be addressed during the write process and thus, by
a factor of
o2, more pixels than before. Correspondingly, the area bi1 with the size of an aperture
image b×b is associated with
o2 = 4 pixels in the case of oversampling with
o=2 in Fig. 6B (also called "double grid"). Of course,
o may take any other integer value as well, in particular 4 ("quad grid"), or also
a non-integer value greater one, such as √2 = 1.414.
[0058] The pixel positions in the placement grids may be divided into two or more groups,
referred to as "partial grids". For instance, the pixels of the placement grid of
Figs. 6A may belong to two partial grids, namely, in an alternating manner according
to a checker-board. Placement grids are further explained in
US 8,222,621, and partial grids are discussed in
US 2015-0028230 A1 in more detail, and the skilled person is referred to those documents with regard
to placement grids and partial grids, respectively; the disclosure of those two documents
with regard to placement grids and partial grids, respectively, is herewith included
by reference.
[0059] Figs. 7A to 7c show an exposure scheme of the pixels for exposing an area on the
target which is suitable for the invention. Shown is a sequence of frames, with increasing
time from top (earlier) to bottom (later). The parameter values in this figure are
o=1, N=2; also, a rectangular beam array is assumed with MX = 8 and MY = 6. The target
moves continuously to the left, whereas the beam deflection is controlled with a seesaw
function as shown on the left side of the figure. During each time interval of length
T1, the beam image stays fixed on a position on the target (corresponding to a position
of a "placement grid"). Thus, the beam image is shown to go through a placement grid
sequence p11, p21, p31. One cycle of placement grids is exposed within a time interval
L/v = NMb/v, by virtue of the target motion v. The time T1 for exposure at each placement
grid corresponds to a length L
G = vT1 = L/(N
o)
2 = bM/N
o2, which we call "exposure length".
[0060] The beamlets are moved over the distance of L
G during the exposure of one set of image elements together with the target. In other
words, all beamlets maintain a fixed position with regard to the surface of the substrate
during the time interval T1. After moving the beamlets with the target along distance
L
G, the beamlets are relocated instantaneously (within a very short time) to start the
exposure of the image elements of the next placement grid. After a full cycle through
the positions p11...p31 of a placement grid cycle, the sequence starts anew, with
an additional longitudinal offset L = bNM parallel to the X direction (scanning direction).
At the beginning and at the end of the stripe the exposure method may not produce
a contiguous covering, so there may be a margin of length L that is not completely
filled.
[0061] With this method it is possible to write stripes of arbitrary length, exposing all
pixels of one partial grid G1, as shown in Fig. 7B for the example of stripe s11 associated
with grid G1. At the beginning and at the end of the stripe the exposure method may
not produce a contiguous covering, so there is a margin mr of width L-L
G that is not completely filled.
[0062] As illustrated in Fig. 7c, the exposure of the pixels belonging to the other partial
grid G2 (or the other partial grids, in case the number of grids is >2) is done by
writing another stripe s21. In the context of the invention, the placement of the
stripes of different grids may be with an offset perpendicular to the scanning direction.
Within the area of overlap of the stripes s11, s21, the pixels thus exposed can combine
into a complete coverage of the pixels to be exposed. However, the stripes s11, s21
will generally not be exposed in immediately successive order, as explained in more
detail below.
[0063] The size of a single aperture image formed on the target is aX/R, where aX is the
opening width of the apertures in the aperture array plate (AAP) and R is the reduction
factor of the charged-particle projection optics.
[0064] Referring to Figs. 8A-8C, each exposure spot 60 corresponding to an aperture image
bi0, bi1 (Fig. 6A,B) is exposed with discrete dose levels as will be discussed in
more detail below. Figs. 8A-C illustrate various overlap configurations of special
interest.
[0065] Fig. 8A depicts the "Double-Grid" multi-beam exposure as discussed above with Fig.
6B, where the overlap between the exposure spots is half of the beam spot size in
X as well as in Y direction as shown in Fig. 8A. In this case the physical grid size
61 is half of the linear size of the spots 60.
[0066] In the "Quad-Grid" multi-beam exposure illustrated in Fig. 8B, the overlap between
the spots is 1/4 of the beam spot size in X as well as in Y direction. In this case
the physical grid size 62 is a quarter of the spot size width.
[0067] Fig. 8c depicts another grid layout, where in addition to Double Grid overlapping
beam exposures, beam exposures are done in the centers in between. Therefore, the
physical grid size 63 is 1/2
3/2 (i.e., √2/4) of the linear spot size. This multi-beam exposure mode is called "Centered-Double-Grid".
[0068] Fig. 9 illustrates the exposure of one exposure spot with a maximum dose level. In
the exemplary case of a 4bit coding, there are 16 dose levels (0,1, 2, ....15), i.e.
the maximum dose level is the sum of 15 dose level increments 64.
[0069] Fig. 10 shows the ideal intensity profile 71 for a line of a width 30 nm, in the
idealized case of zero blur. When using "Quad-Grid" multi-beam exposure the overlap
is a quarter of the beam size. Thus, for the case of 20 nm beam size the physical
grid size is 5 nm. A discrete dose level can be assigned to each area of the physical
grid, which is 5 nm × 5 nm for the example chosen; the line 72 in Fig. 10 indicates
the superposition of the intensity (or total dose) as it is composed of the overlapping
exposure spots with discrete dose levels assigned to the pixel positions for generating
the 30 nm line, whereas for better visibility the blur has been set to zero (so that
the dose distribution of a single exposure spot becomes a rectangle). If the blur
has a realistic value such as shown in Fig. 13, the step function at the edge of the
rectangle is convoluted with a Gaussian function, which eventually transforms to a
Gaussian shape. In that sense the line 72 can be seen as superposition of Gaussian
functions at blur zero. In the general case the dose level histogram will not be symmetrical
in order to position the left and right edge at predefined positions.
[0070] Fig. 11 shows a simulation for a line of 30.0 nm width, with the left edge to be
positioned at 0.0 nm and the right edge at 30.0 nm. For the simulation, it was assumed
that beam spots of 20 nm are exposed with 5.1 nm 1sigma blur (i.e., 12.0 nm FWHM blur).
The intensity profile 76 is formed by overlapping the profiles of the exposure spots
73, 74, and 75. The dose level of the leftmost exposure spot 74 is adjusted such that
the 30 nm line starts at the desired start position 77, i.e. at 0 nm. The dose level
of the rightmost exposure spot 75 is adjusted such that exposed line ends at position
78 at 30.0 nm. As can be seen in Fig. 11, in accordance with "Quad-Grid" exposure,
the overlap of the exposure spots 73, 74, 75 is a quarter of the beam size, i.e. 5
nm.
[0071] Figs. 12A and 12B illustrate how the invention enables the MBW device to write lines
with precise edge definitions; in each figure, the top frame shows the edge position
error vs. line width, the middle frame the intensity profile, and the bottom frame
shows the edge position deviation when enhancing the exposure dose by 10% vs. line
width. Fig. 12A shows the intensity profile obtained for a 31.4 nm line width, and
Fig. 12B for a 40.0 nm line width. Using the MBW with 20 nm beam size and Quad-Grid
exposure (5nm physical grid size), the line width of the structure generated by the
exposure can be changed in steps of 0.1 nm. Because of the integer dose levels there
are slight deviations from the 0.1 nm address grid. These deviations are indicated
as "edge position error" (top frames), as functions of the desired line width, in
0.1 nm steps between 30.0 nm and 40.0 nm. As can be seen the deviations are within
±0.05 nm. Furthermore, the change of edge position with 10% change of dose is only
approx. 1 nm, varying only slightly with change of line width as shown in the bottom
frames. In other words, since the dose is controlled in a MBW to better than 1%, the
change of edge position with 1% change of dose is within approx. one atomic layer.
[0072] Fig. 13 illustrates a most important advantage of the MBW, namely, that the line
width is virtually independent of blur at the 50% dose threshold. Shown in Fig. 13
are the intensity profile 71 for zero blur, the dose level histogram 72, and resulting
intensity profiles 81, 82, 83 calculated with 3.5 nm, 5.0 nm, and 7.5 nm 1sigma blur,
respectively. The edge positions 73 and 74 of the generated structure are where the
zero blur intensity profile 71 crosses the "0.5" intensity level. The enlarged detail
of Fig. 13A shows the region around the position 73 at the left-side flank. The dose
level assignments 72 are for using 20 nm beam size with 1sigma blur of 5 nm and Quad-Grid
multi-beam exposure, providing a 5 nm physical grid size.
[0073] Figs. 14A, 14B, and 14C show intensity profile diagrams illustrating how the multi-beam
exposure methods illustrated here can achieve a fine positioning of structure feature
with resolution smaller than the grid size. In the intensity profile diagrams, like
those of Figs. 14A-C, the discrete dose levels are visualized as rectangles 64 of
uniform height, piled up in a "brick-layer" arrangement; of course, this "brick-layer"
depiction is only symbolical and intended to facilitate interpretation of the drawings.
[0074] Fig. 14A shows a dose level histogram, for the example of a line of 30nm width exposed
by means of a 4bit (i.e., 15 dose levels per spot) exposure in a Quad-Grid with a
beam spot size of 20nm width. The grid size 62 is 1/4 of the linear size of the exposure
spots, which are symbolized as rectangles piled up in a "brick-layer" arrangement,
and the resulting dose level distribution 65 is outlined as a bold line.
[0075] The line width can be made smaller or larger in very fine steps, which are smaller
than the grid size, in this case the Quad-Grid size 62. Reducing the line width can
be achieved by lowering the dose level of the outermost exposure spots and/or omitting
exposure spots (the latter when the reduction is at least about one half of a exposure
spot size). Increasing the line width can be achieved by enhancing the dose level
of the outermost exposure spots and/or, in particular when the maximum dose level
has been reached, to add an additional, preferably overlapping, exposure spot. The
latter aspect is illustrated in Fig. 14B: an exposure spot 66 having a defined dose
level is added, resulting in a dose level histogram 67 for the line with larger width
compared to 65. By combining these effects of decreasing and increasing on either
side, there is also the possibility to shift the line position in very fine steps.
Fig. 14C illustrates a shift of the line without changing the width, which is achieved
by removing dose levels from spot 68 and adding corresponding dose levels to spot
69, resulting in the dose level histogram 70 which corresponds to a line shifted to
the right as compared to the line of Fig. 14A.
[0076] The intensity profiles of Figs. 14A-C are shown along the X direction of the target
plane. It is straightforward to extend the multi-beam exposure methods illustrated
here to lines along other directions as well, and fine positioning can be achieved
for lines on the target plane with any direction.
[0077] A first aspect of the invention relates to a method of exposing the target area,
based on writing of stripes as discussed above in Figs. 7A-C, where the same target
area is covered by more than one set of stripes, referred to as passes. Each pass
includes a set of stripes which, taken as a whole cover the target area, by exposing
the exposure spots that belong to one of the partial grids, respectively. For instance,
in the case of two partial grids the first pass exposes the exposure spots belonging
to a first partial grid, and the second pass exposes those of a second partial grid.
In addition, the position of the stripes of different passes are offset to each other
so stripes of one pass cover the boundary margin between stripes of another pass.
[0078] This principle is illustrated in the following by an exemplary embodiment, which
implements a method which is also referred to as "Double-Pass-at-50%-Overlap".
[0079] Fig. 15 shows the exemplary embodiment 90 of the "Double-Pass-at-50%-Overlap" multi-beam
exposure method. This method provides an improved arrangement of the exposure stripes
100 within the substrate field where a desired pattern is to be exposed, while allowing
for a reduction, possibly minimization, of errors due to imaging or alignment deviations.
The multi-beam exposure of the substrate field starts with exposing stripe 91 with
a width 92. In the example of a beam array field of 82µm × 82µm, as realized in a
multi-beam mask writer of the applicant, this width 92 is 82µm. The symmetry line
of stripe 91 is indicated as a dash-dotted line, at a distance 93 from the boundaries
of stripe 91. The stripe has a length 94; e.g., for a mask exposure field this length
94 is 132mm. The next stripe 95, again with width 92 is exposed with an overlap of
width 96 as outlined in
patent US 8,378,320 B2 of the applicant. As an example this width 96 is 2µm so that the distance 109 between
the symmetry lines of stripe 91 and strip4 95 is 80µm. Thus, the distance 109 is an
"effective stripe width". The procedure continues with stripes 97, 98, 99 and so on,
covering the area to be exposed in a first pass of stripes.
[0080] A second set of stripes 101,104,106,107,108 etc. is exposed with 50% overlap as shown
in Fig. 15. These stripes form a second pass covering the area to be exposed on the
target (except possibly for, albeit small, margins at the edge of the area). The stripe
width 102 is the same as the width 92 of the stripes of the first pass. The upper
boundary of stripe 101 is shifted by a distance 103 from the symmetry line of stripe
91, so the stripe 101 covers the latter line. This distance 103 is half of distance
96.
[0081] The stripes 101 and 104 are exposed with a small overlap region 105, where the distance
105 is preferably the same as distance 96.
[0082] In Fig. 15 the stripes 100 are shown in a staggered arrangement, i.e. shifted in
the X-direction, only for viewing purpose, in order to improve the clarity of what
is shown; it will be understood that in a realistic multi-beam exposure the stripes
align and are typically covering the same length along their common direction (in
this case, the x-direction).
[0083] Fig. 16 shows how exposure spots may be exposed using two partial grids with the
example of the "Double-Pass-at-50%-Overlap" method in the case of "Double-Grid" multi-beam
writing 120. The first pass stripes 91, 96-99 are written by exposing exposure spots
121, which are symbolized by centers 122 with a narrow checked hatching as illustrated
in the insert of Fig. 16A, whereas the second pass stripes 101, 104, 106-108, which
are arranged at a 50% overlap with the stripes of the first pass, are made exposing
exposure spots 121 symbolized by centers 123 depicted with a wider checked hatching,
cf. the insert of Fig. 16B.
[0084] Fig. 17 illustrates another example, namely, for the analogous case 130 for "Centered-Double-Grid"
multi-beam exposure. The exposure spots are again symbolized by checked hatchings
as depicted in Figs. 16A+B.
[0085] Fig. 18 shows a further example, namely, for the analogous case 140 for "Quad-Grid"
multi-beam exposure of multiple stripes composed of exposure spots 121 using again
the checked hatched symbols of Figs. 16A+B.
[0086] This "Quad-Grid" example is illustrated in more detail in Figs. 19 to 21: Fig. 19
shows a first sequence 150 of stripe exposures comprising: stripe exposures 151 and
153, with exposure spots 121 denoted by their respective centers 122a, with a hatching
as depicted Fig. 19A; and stripe exposures 152 and 154, with exposure spots 121 denoted
by their respective centers 122b, see Fig. 19B. Figure 20 shows a second sequence
160 comprising: overlapping stripe exposures 161 and 163, with exposure spots 121
denoted by their respective centers 123a, cf. Fig. 20A; and stripe exposures 162 and
164, with exposure spots 121 denoted by their respective centers 123b, cf. Fig. 20B.
[0087] Finally, Fig. 21 shows the complete exposure 170 as generated by overlapping the
exposures of Fig. 19 and Fig. 20 according to the "Double-Pass-at-50%-Overlap".
[0088] The stripes are written in several sweeps, for instance two sweeps, which employ
different writing directions for the stripes belonging to the respective sweep while
each sweep covers the exposure area on the target. In other words, the stripes in
each sweep run basically parallel, but with different general direction for each sweep.
The term "general direction" is meant to refer to both ways of moving along a given
direction on the target plane, such as ±x or ±y, where the symbol ± denotes that both
ways belong to the same general direction. Each sweep contains a number of stripes,
i.e. at least one stripe, but usually a plurality of stripes with a considerable number
depending on the respective application and pattern to be written.
[0089] Fig. 22 illustrates an embodiment of the "Bi-Directional-Double-Pass" multi-beam
exposure method according to the invention. The reference R2 denotes an exposure area
on the target; it has dimensions Rx × Ry as measured along the x- and y-directions,
respectively. In a first sweep, stripes 181, 182, ... 183, are written, which extend
along one direction d1 (along ±x, horizontal in Fig. 22) and have widths y0, where
the width is measured across the corresponding direction of extension ("general direction")
of the stripe. At the end of each stripe (but the last) the target stage turns to
the start of the next stripe, preferably combined with a reversal of direction while
maintaining the general direction d1; thus performing end turns 184,185 ... between
the stripes. Then a second sweep is carried out, in which stripes 187, 188, 189...
are written; these stripes extend along the perpendicular direction d2 (along ±y,
vertical in Fig. 22) and have widths x0. Between the stripes of the second sweep,
stage turns 186 are performed. Thus, between sweeps the general direction d1, d2 is
changed; in other words each sweep is associated with a specific general direction.
[0090] Further in Fig. 22, the stripe 189, which belongs to the second sweep, is depicted
in the progress of being written: An area 190 is shown which is just being written
as part of the perpendicular stripe 189. Fig. 23 shows an enhanced view of the area
at the cross-border between horizontal stripes 181 and 182, and vertical stripes 188
and 189. In this depiction, the exposure spots 121 with center by circles 122 correspond
to stripe exposures 181,182, etc.; and the exposure spots 121 with centers 123 symbolize
vertical stripe exposures 188 and 189 filling in the space 190.
[0091] The "Bi-Directional-Double-Pass" multi-beam exposure according to the invention provides
an enhanced coverage to reduce stripe boundary errors.
[0092] The stripes 181, ... 183 of the first sweep are written with half the exposure dose,
whereas the stripes 187, 188, 189, ... of the second sweep provide the other half
of the exposure dose. Therefore, with a given data path rate, the stripe exposures
can be done at double stage velocity speed. Thus, the writing time for the exposure
field R2 is the same as compared to single pass writing with the full spot coverage.
With respect to overall writing time, the Double-Pass methods may have somewhat higher
stage return overheads, which can be kept sufficiently low to be negligible.
[0093] While the depiction of Fig. 23 is with regard to the Bi-Directional for the case
of Quad-Grid multi-beam writing, it will be evident for the skilled person to adapt
the Bi-Directional-Double-Pass multi-beam exposure for the Double-Grid and the Centered-Double-Grid
multi-beam exposure techniques in an analogous way.
[0094] In the case of two sweeps, the two general directions d1, d2 may be oriented perpendicular
to each other, in particular at 90°, for instance ±x, ±y coinciding with the x- and
y-directions of the target stage. Generally, the number of sweeps may be more than
two. The general directions may be different for each sweep, for instance at angles
smaller than 90°. Alternatively or in combination, the general direction of non-consecutive
sweeps may be the same, for instance in a sequence like ±x, ±y, ±x, ±y for four sweeps.
[0095] As pointed out in
US 2015/0028230 A1 it is not necessary that the exposures of stripes 181, ...183 belonging to the same
sweep be done one after the other, but may be done in groups, e.g. of three stripes
each, with a distance between the groups as shown in Fig. 24A, where the distance
between the groups of stripes is such that an integer of stripe groups fits in between.
Fig. 24B shows the exposure of the second groups of three stripes each for this example.
This method can be implemented for the vertical stripes as well. Of course, the number
of stripes in each group may take any suitable integer value.
[0096] With the present invention and methods disclosed here a further reduction of errors
can be achieved, in particular with respect to substrate heating.
1. A method for irradiating a target with a beam of energetic radiation formed by electrically
charged particles, comprising the steps of
- providing a pattern definition device (4) having a plurality of apertures (24) transparent
to said radiation,
- illuminating said pattern definition device by means of an illuminating wide beam
(lb), which traverses the pattern definition device through said apertures thus forming
a patterned beam (pb) consisting of a corresponding plurality of beamlets,
- forming said patterned beam into a pattern image (pm) on the location of the target
(17), said pattern image comprising the images (b1) of at least part of the plurality
of apertures covering a number of pattern pixels (px) on the target, and
- generating a relative movement between said target (16) and the pattern definition
device (4) producing a movement of said pattern image on the target along a path over
a region (R1, R2) where a beam exposure is to be performed, said path being composed
of sections which each extend along a general direction (d1, d2), said region being
composed of a plurality of pattern pixels (px) arranged in a regular arrangement and
said region having a total width (Ry, Rx) as measured across said general direction
(d1, d2), the movement along said path defining a number of stripes (s1-sn; 181-183;
187-189) covering said region in sequential exposures,
wherein the number of stripes are written in at least two sweeps, each sweep having
a respective general direction (d1, d2), and the general direction being changed between
sweeps, wherein each stripe belongs to exactly one of said sweeps,
wherein the stripes in each sweep run substantially parallel to each other along the
respective general direction, the stripes having respective widths (y0, x0) as measured
across said main direction, and for each sweep the widths (y0, x0) of the stripes
of one sweep combining into a cover of the total width (Ry, Rx).
2. The method of claim 1, wherein each sweep is associated with one of a number of partial
grids (G1, G2) of pattern pixels which are exposable during the respective sweep,
the partial grids (G1, G2) being mutually different and, when taken together, combining
to the complete plurality of pattern pixels (px) which are comprised in said region
where a beam exposure is to be performed.
3. The method of claim 1 or 2, wherein groups of stripes belonging to the same sweep
are written subsequently in time.
4. The method of any one of claims 1 to 3, wherein stripes written with the same general
direction are written with alternating orientation of said general direction.
5. The method of any one of claims 1 to 4, wherein the stripes of each sweep have uniform
width (y0, x0).
6. The method of any one of claims 1 to 5, wherein within each sweep the stripes are
exposed at lateral offsets to each other which correspond to the respective widths
(y0) of the stripes.
7. The method of any one of claims 1 to 5, wherein the stripes of at least one of the
sweeps, preferably of all sweeps, are overlapping, wherein in the range of overlap
(96) of two stripes (s11, s21) of the same sweep:
nominal positions of pattern pixels of one of the two stripes are overlapping with
nominal positions of corresponding pattern pixels of the other of the two stripes,
and
pattern pixels are exposed in the two overlapping stripes in a complementary manner
with regard to the pattern to be imposed.
8. The method of any one of the preceding claims, wherein the general directions (d1,
d2) of consecutive sweeps are in a right angle to each other.
9. The method of any one of the preceding claims, wherein the number of stripes are written
in two sweeps.
10. The method of any one of the preceding claims, wherein in at least one of the sweep,
preferably in each sweep, a plurality of stripes is written,
wherein the plurality of stripes of each sweep are distributed into at least two groups
of spatially adjacent stripes, and the stripes are written either in a time sequence
wherein either each stripe is followed by a non-adjacent stripe of a different group,
or in a time sequence wherein the stripes are written in groups of stripes according
to the order of the groups, with each group of stripes being followed by a non-adjacent
different group.
11. The method of any one of the preceding claims, wherein during generating the relative
movement between the target (16) and the pattern definition device (4) a target stage
(6) is used, said target stage (6) being configured to continuously move the target
(16) along at least two of the general directions, wherein an offset from a nominal
position, which offset occurs during a movement by a first distance along either of
said at least two of the general directions, is always less than a fraction of the
first distance, said fraction being in the order of 0.001.
12. Charged-particle multi-beam processing apparatus (1) for exposure of a target (16)
by means of a structured beam of electrically charged particles, comprising:
- an illumination system (3),
- a pattern definition device (4),
- a projection optics system (5), and
- a target stage (6),
the illumination system (3) being configured to produce a beam of said electrically
charged particles and form it into an illuminating wide beam (lb) illuminating the
pattern definition device (4), the pattern definition device (4) being configured
to form the shape of the illuminating beam into a patterned beam composed of a plurality
of beamlets, and the projection optics system (5) being configured to form said patterned
beam into a pattern image (pm) on the location of the target (17), thus exposing a
plurality of pattern pixels (px) on the target,
the target stage (6) being configured to generate a relative movement between said
target (16) and the pattern definition device (4),
wherein said apparatus is configured to perform the method of any of claims 1 to 11.
13. Charged-particle multi-beam processing apparatus of claim 12, wherein said target
stage (6) is configured to continuously move the target (16) along at least two of
the general directions, wherein an offset from a nominal position, which offset occurs
during a movement by a first distance along either of said at least two of the general
directions, is always less than a fraction of the first distance, said fraction being
in the order of 0.001.
14. Charged-particle multi-beam processing apparatus of claim 13, wherein said target
stage comprises air bearings enabling high stage velocity in an X and a Y direction
in the target plane.
1. Verfahren zum Belichten eines Target mit einem Strahl energiereicher, aus elektrisch
geladenen Teilchen gebildeter Strahlung, mit den Schritten
- Bereitstellen einer Musterdefinitionsvorrichtung (4) mit einer Vielzahl von für
die Strahlung transparenten Aperturen (24),
- Beleuchten der Musterdefinitionsvorrichtung mittels eines breiten Beleuchtungsstrahls
(lb), der die Musterdefinitionsvorrichtung durch die Aperturen durchläuft und so einen
strukturierten Strahl (pb) bildet, der aus einer entsprechenden Vielzahl von Teilstrahlen
besteht,
- Formen des strukturierten Strahls in ein Muster-Bild (pm) auf dem Ort des Target
(17), wobei das Muster-Bild die Bilder (b1) von zumindest einem Teil der Vielzahl
von Aperturen umfasst und eine Anzahl von Muster-Pixels (px) auf dem Target überstreicht,
- Herstellen einer relativen Bewegung zwischen dem Target (17) und der Musterdefinitionsvorrichtung
(4), wobei eine Bewegung des Muster-Bildes entlang einer Bahn auf dem Target über
einen Bereich (R1, R2), in dem eine Strahlbelichtung durchgeführt werden soll, erzeugt
wird, wobei die Bahn aus Abschnitten besteht, die jeweils entlang einer Allgemeinrichtung
(d1, d2) verlaufen, wobei dieser Bereich sich aus einer Vielzahl von in einer regelmäßigen
Anordnung angeordneten Muster-Pixels (px) zusammensetzt und eine Gesamtbreite (Ry,
Rx) gemessen quer zur Allgemeinrichtung (d1, d2) aufweist, wobei die Bewegung entlang
der Bahn eine Anzahl von Streifen (s1-sn; 181-183; 187-189) definiert, die diesen
Bereich in fortlaufenden Belichtungen überstreichen,
wobei die Anzahl von Streifen in zumindest zwei Durchläufen geschrieben werden, wobei
jeder Durchlauf eine jeweilige Allgemeinrichtung (d1, d2) hat, und die Allgemeinrichtung
zwischen Durchläufen gewechselt wird,
wobei jeder Streifen zu genau einem der Durchläufe gehört,
wobei die Streifen in jedem Durchlauf im Wesentlichen parallel zueinander entlang
der jeweiligen Allgemeinrichtung verlaufen, wobei die Streifen jeweils eine Breite
(y0, x0) gemessen quer zur Allgemeinrichtung haben und für jeden Durchlauf die Breiten
(y0, x0) der Streifen eines Durchlaufs zu einer Überdeckung der Gesamtbreite (Ry,
Rx) zusammentreten.
2. Verfahren nach Anspruch 1, wobei jedem Durchlauf eines aus einer Anzahl von Teilgittern
(G1, G2) von Muster-Pixels zugeordnet ist, die während des jeweiligen Durchlaufs belichtbar
sind, wobei die Teilgitter (G1, G2) zueinander verschieden sind und zusammengenommen
zu der vollständigen Vielzahl von Muster-Pixels (px) zusammentreten, die in besagtem
Bereich, in dem eine Strahlbelichtung durchgeführt werden soll, enthalten sind.
3. Verfahren nach Anspruch 1 oder 2, wobei Gruppen von Streifen, die zu demselben Durchlauf
gehören, zeitlich aufeinanderfolgend geschrieben werden.
4. Verfahren nach einem der Ansprüche 1 bis 3, wobei Streifen, die mit derselben Allgemeinrichtung
geschrieben werden, mit alternierender Orientierung dieser Allgemeinrichtung geschrieben
werden.
5. Verfahren nach einem der Ansprüche 1 bis 4, wobei die Streifen jedes Durchlaufs gleiche
Breite (y0, x0) aufweisen.
6. Verfahren nach einem der Ansprüche 1 bis 5, wobei in jedem Durchlauf die Streifen
mit seitlichem Versatz zueinander belichtet werden, der der jeweiligen Breite (y0)
der Streifen entspricht.
7. Verfahren nach einem der Ansprüche 1 bis 5, wobei die Streifen von zumindest einem
der Durchläufe, vorzugsweise aller Durchläufe, einander überlappen, wobei in dem Uberlappungsbereich
(96) von zwei Streifen (s11, s21) desselben Durchlaufs:
nominelle Positionen von Muster-Pixels eines der beiden Streifen mit nominellen Positionen
entsprechender Muster-Pixels des anderen der beiden Streifen überlappen, und
Muster-Pixel in den beiden überlappenden Streifen in komplementärer Weise hinsichtlich
des auszuübenden Musters belichtet werden.
8. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Allgemeinrichtungen (d1,
d2) aufeinanderfolgender Durchläufe in rechtem Winkel zueinander liegen.
9. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Anzahl von Streifen in
zwei Durchläufen geschrieben werden.
10. Verfahren nach einem der vorhergehenden Ansprüche, wobei in zumindest einem der Durchlauf,
vorzugsweise in allen Durchläufen, eine Vielzahl von Streifen geschrieben wird,
wobei die Vielzahl von Streifen jedes Durchlaufs in zumindest zwei Gruppen räumlich
nebeneinanderliegender Streifen aufgeteilt ist, und die Streifen geschrieben werden:
entweder in einer zeitlichen Abfolge, bei der auf jeden Streifen ein nicht daneben
liegender Streifen einer anderen Gruppe folgt, oder in einer zeitlichen Abfolge, bei
der die Streifen in Gruppen von Streifen gemäß der Ordnung der Gruppen - wobei auf
jede Gruppe von Streifen eine nicht daneben liegende andere Gruppe folgt - geschrieben
werden.
11. Verfahren nach einem der vorhergehenden Ansprüche, wobei während des Herstellens der
relativen Bewegung zwischen dem Target (16) und der Musterdefinitionsvorrichtung (4)
eine Target-Station (6) verwendet wird, welche dazu eingerichtet ist, das Target (16)
entlang zumindest zweier der Allgemeinrichtungen kontinuierlich zu bewegen, wobei
eine Versetzung gegenüber einer Sollposition, die während einer Bewegung um einen
ersten Abstand entlang je einer der zumindest zwei der Allgemeinrichtungen auftritt,
immer geringer ist als ein Bruchteil des ersten Abstands, wobei dieser Bruchteil in
der Größenordnung von 0,001 ist.
12. Multi-Strahl-Bearbeitungsgerät (1) mit geladenen Teilchen zur Belichtung eines Target
(16) mittels eines strukturierten Strahls elektrisch geladener Teilchen, aufweisen:
- ein Beleuchtungssystem (3),
- ein Musterdefinitionsvorrichtung (4),
- eine Projektionsoptik (5), und
- eine Target-Station (6),
wobei das Beleuchtungssystem (3) dazu eingerichtet ist, einen Strahl der elektrisch
geladenen Teilchen zu erzeugen und in einen breiten Beleuchtungsstrahl (lb) zu formen,
der die Musterdefinitionsvorrichtung (4) beleuchtet, wobei die Musterdefinitionsvorrichtung
(4) dazu eingerichtet ist, die Form des Beleuchtungsstrahls in einen strukturierten
Strahl zu formen, der aus einer Vielzahl von Teilstrahlen besteht, und wobei die Projektionsoptik
(5) dazu eingerichtet ist, den strukturierten Strahl in ein Muster-Bild (pm) auf dem
Ort des Target (17) zu formen und so eine Vielzahl von Muster-Pixels (px) auf dem
Target zu belichten,
wobei die Target-Station (6) dazu eingerichtet ist, eine relative Bewegung zwischen
dem Target (17) und der Musterdefinitionsvorrichtung (4) herzustellen,
wobei das Gerät zum Ausführen des Verfahrens nach einem der Ansprüche 1 bis 11 eingerichtet
ist.
13. Multi-Strahl-Bearbeitungsgerät (1) mit geladenen Teilchen nach Anspruch 12, wobei
die Target-Station (6) dazu eingerichtet ist, das Target (16) entlang zumindest zweier
der Allgemeinrichtungen kontinuierlich zu bewegen, wobei eine Versetzung gegenüber
einer Sollposition, die während einer Bewegung um einen ersten Abstand entlang je
einer der zumindest zwei der Allgemeinrichtungen auftritt, immer geringer ist als
ein Bruchteil des ersten Abstands, wobei dieser Bruchteil in der Größenordnung von
0,001 ist.
14. Multi-Strahl-Bearbeitungsgerät (1) mit geladenen Teilchen nach Anspruch 13, wobei
die Target-Station Luftlager umfasst, die eine große Geschwindigkeit der Station in
einer X- und einer Y-Richtung in der Ebene des Target ermöglicht.
1. Procédé pour irradier une cible avec un faisceau de rayonnement énergétique formé
par des particules chargées électriquement, comprenant les étapes :
- disposer un dispositif de définition de motif (4) comprenant une pluralité d'ouvertures
(24) transparentes audit rayonnement,
- éclairer ledit dispositif de définition de motif au moyen d'un faisceau large d'éclairage
(lb), qui traverse le dispositif de définition de motif à travers lesdites ouvertures,
formant ainsi un faisceau à motif (pb) consistant en une pluralité correspondante
de petits faisceaux,
- former ledit faisceau à motif dans une image de motif (pm) sur l'emplacement de
la cible (17), ladite image de motif comprenant les images (b1) d'au moins une partie
de la pluralité d'ouvertures couvrant un nombre de pixels de motif (px) sur la cible,
et
- générer un mouvement relatif entre ladite cible (16) et le dispositif de définition
de motif (4), produisant un mouvement de ladite image de motif sur la cible le long
d'un trajet sur une région (R1, R2) où une exposition au faisceau doit être réalisée,
ledit trajet étant composé de sections qui s'étendent chacune le long d'une direction
générale (d1, d2), ladite région étant composée d'une pluralité de pixels de motif
(px) disposés selon un arrangement régulier et ladite région ayant une largeur totale
(Ry, Rx) telle que mesurée en travers de ladite direction générale (d1, d2), le mouvement
le long dudit trajet définissant un nombre de bandes (s1-sn ; 181-183 ; 187-189) couvrant
ladite région dans des expositions séquentielles,
le nombre de bandes étant écrit en au moins deux balayages, chaque balayage ayant
une direction générale respective (d1, d2), et la direction générale étant changée
entre les balayages,
chaque bande appartenant à exactement un desdits balayages, les bandes dans chaque
balayage s'étendant de manière sensiblement parallèle les unes aux autres le long
de la direction générale respective, les bandes ayant des largeurs respectives (y0,
x0) telles que mesurées en travers de ladite direction principale, et pour chaque
balayage les largeurs (y0, x0) des bandes d'un balayage se combinant en une couverture
de la largeur totale (Ry, Rx).
2. Procédé selon la revendication 1, dans lequel chaque balayage est associé à une parmi
un nombre de grilles partielles (G1, G2) de pixels de motif qui sont aptes à être
exposées au cours du balayage respectif, les grilles partielles (G1, G2) étant différentes
les unes des autres et, lorsqu'elles sont prises ensemble, se combinent à l'ensemble
de la pluralité de pixels de motif (px) qui sont compris dans ladite région où une
exposition au faisceau doit être réalisée.
3. Procédé selon la revendication 1 ou 2, dans lequel des groupes de bandes appartenant
au même balayage sont écrits de manière subséquente dans le temps.
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel les bandes écrites
avec la même direction générale sont écrites avec une orientation alternée de ladite
direction générale.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel les bandes de
chaque balayage ont une largeur uniforme (y0, x0).
6. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel, dans chaque
balayage, les bandes sont exposées au niveau de décalages latéraux les unes par rapport
aux autres, lesquels correspondent aux largeurs respectives (y0) des bandes.
7. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel les bandes d'au
moins un des balayages, de préférence de tous les balayages, se chevauchent, dans
lequel dans la plage de chevauchement (96) de deux bandes (s11, s21) du même balayage
:
des positions nominales de pixels de motif de l'une des deux bandes chevauchent des
positions nominales de pixels de motif correspondants de l'autre des deux bandes,
et
des pixels de motif sont exposés dans les deux bandes se chevauchant, d'une manière
complémentaire par rapport au motif à imposer.
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel les directions
générales (d1, d2) de balayages consécutifs sont à angle droit l'une de l'autre.
9. Procédé selon l'une quelconque des revendications précédentes, dans lequel le nombre
de bandes est écrit en deux balayages.
10. Procédé selon l'une quelconque des revendications précédentes, dans lequel, dans au
moins un des balayages, de préférence dans chaque balayage, une pluralité de bandes
est écrite,
la pluralité de bandes de chaque balayage étant répartie dans au moins deux groupes
de bandes spatialement adjacentes, et les bandes étant écrites soit dans une séquence
de temps où chaque bande est suivie par une bande non adjacente d'un groupe différent,
soit dans une séquence de temps où les bandes sont écrites en groupes de bandes conformément
à l'ordre des groupes, avec chaque groupe de bandes suivi par un groupe différent
non adjacent.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel, lors de
la génération du mouvement relatif entre la cible (16) et le dispositif de définition
de motif (4), une platine de cible (6) est utilisée, ladite platine de cible (6) étant
configurée pour déplacer de manière continue la cible (16) le long d'au moins deux
des directions générales, un décalage vis-à-vis d'une position nominale, lequel décalage
se produit au cours d'un mouvement d'une première distance le long de l'une ou l'autre
des au moins deux directions générales, étant toujours inférieur à une fraction de
la première distance, ladite fraction étant de l'ordre de 0,001.
12. Appareil de traitement à multi-faisceaux de particules chargées (1) pour l'exposition
d'une cible (16) au moyen d'un faisceau structuré de particules chargées électriquement,
comprenant :
- un système d'éclairage (3),
- un dispositif de définition de motif (4),
- un système d'optique de projection (5), et
- une platine de cible (6),
le système d'éclairage (3) étant configuré pour produire un faisceau desdites particules
chargées électriquement et pour le former en un faisceau large d'éclairage (lb) éclairant
le dispositif de définition de motif (4), le dispositif de définition de motif (4)
étant configuré pour former la forme du faisceau d'éclairage en un faisceau à motif
composé d'une pluralité de petits faisceaux, et le système d'optique de projection
(5) étant configuré pour former ledit faisceau à motif en une image de motif (pm)
sur l'emplacement de la cible (17), exposant ainsi une pluralité de pixels de motif
(px) sur la cible,
la platine de cible (6) étant configurée pour générer un mouvement relatif entre ladite
cible (16) et le dispositif de définition de motif (4),
ledit appareil étant configuré pour mettre en oeuvre le procédé de l'une quelconque
des revendications 1 à 11.
13. Appareil de traitement à multi-faisceaux de particules chargées selon la revendication
12, dans lequel ladite platine de cible (6) est configurée pour déplacer de manière
continue la cible (16) le long d'au moins deux des directions générales, un décalage
vis-à-vis d'une position nominale, lequel décalage se produit au cours d'un mouvement
d'une première distance le long de l'une ou l'autre des deux directions générales,
étant toujours inférieur à une fraction de la première distance, ladite fraction étant
de l'ordre de 0,001.
14. Appareil de traitement à multi-faisceaux de particules chargées selon la revendication
13, dans lequel ladite platine de cible comprend des paliers à air permettant une
haute vitesse de platine dans une direction X et une direction Y dans le plan de la
cible.